This invention relates to earth boring apparatus and more particularly to roller stabilizers useful in the rotary system of boring blast holes.
Difficulty has been experienced with stabilizers of the type employing plural colevel rollers mounted on parallel off-axial journals when the hole size is increased, e.g., up to 15 or more inches in diameter. Larger bearing diameters are needed to accommodate the large lateral loads without undue wear. A similar problem arises with roller reamers, which are similar to stabilizers, the latter being undergage while reamers are full gage. A solution to the problem is the employment of tandem rollers mounted on eccentric journals extending around the stabilizer mandrel. Such construction is already known, e.g. for roller stabilizers, as shown in U.S. Pat. No. 3,400,773 to TIRAPOLSKY et al. See also U.S. Pat. No. 1,772,491 to Koppl.
With tandem rollers it is necessary to orient the eccentric journals azimuthally relative to each other in order to distribute the lateral loading uniformly about the axis of the stabilizer mandrel. Otherwise the rollers would cause the mandrel to deflect and reduce the effectiveness of the stabilizer. In this regard Tirapolsky, referring to the elements on which the rollers rotate as hubs, states:
"A suitable assembly can be obtained by connecting the hubs of the consecutive reaming elements by coupling rings in which the hubs are screwed but it is very difficult in this way to obtain a correct relative angular positioning of the axes of the hubs around the axis of the body of the remaining tool. PA1 Another solution is the use of a shaft for the reaming tool on which eccentric hubs are mounted and the rollers turn on these hubs on axes parallel to the shaft with the hubs being fastened to the shaft for rotation either by keying on the shaft or by utilization of a shaft having a polygonal section. PA1 Any of the solutions discussed above require a shaft having a cross-section sufficient to transmit large forces of rotation to the reaming elements. PA1 An object of the present invention is to provide a rigid assembly of reaming elements in which the transmission of the torque to these reaming elements is provided by the assembly itself which is solidly and directly connected to the driving shaft of the bottom motor which drives the tool in rotation."
Tirapolsky employs rings between his hubs, the rings having eccentric sockets to receive and position the hubs, which are largely out of contact with the mandrel.
Koppl employs a polygonal section shaft, as mentioned by Tirapolsky.